Many people choose not to vacuum pack their fresh foods and leftovers because it is much more convenient to simply snap a cover onto the top of a low-cost plastic container and place the container in the refrigerator (provided, of course, a cover that matches the container can be found). Although covering a container helps retain moisture, it does not stop food from oxidizing and losing its fresh taste. The only way to prevent oxidation is to vacuum pack food. Most households have an ample supply of low-cost polyethylene (PE) food containers of various shapes and sizes. However, PE containers can't hold a vacuum because polyethylene continually deforms when placed under load—a phenomenon known as “creep”. Creep can cause any vacuum seal to quickly leak. Accordingly, simply vacuum packing food in low-cost PE consumers is not viable.
However, most households also possess sturdy food containers that can, in fact, hold a vacuum. Such containers are made of either metal, glass, ceramic, glass-ceramic formulations, clay, or stiff plastics such as polycarbonate (PC), ABS, acrylic, and thermoset materials. Accordingly, most households have the option of vacuum packing their food by either placing their food directly in such sturdy containers, or using an indirect approach of placing PE food containers inside more sturdy containers before performing the vacuum packing operation.
People who decide to vacuum pack their foods do so to extract the most value from their purchases. As such, to realize a net savings, the amortized cost of vacuum packing apparatus must be less than the cost of the food that users are trying to preserve. However, because it is very challenging to achieve reliable air-tight seals between un-matched food containers and lids, most vendors sell food containers and vacuum lids only as matched pairs, with a flexible elastomeric gasket affixed to the vacuum lids to create air-tight seals between the two parts. This practice increases the cost of vacuum packing apparatus, thereby reducing the net savings. This practice also increases the space that vacuum packing apparatus takes up in crowded kitchen cabinets and drawers. Further, any theoretical net savings must outweigh the inconvenience and time it takes to perform the vacuum packing operation. Accordingly, vacuum packing systems for home food containers must be usable without employing elaborate ancillary equipment (such as special-purpose vacuum packing machines) that take a significant amount of time to set up and operate. Also, the vacuum packing apparatus should be sufficiently compact to conveniently fit in crowded kitchens. Finally, vacuum packing systems must be reliable and consistently retain vacuums for extended periods.
As previously stated, traditional apparatus for vacuum packing food containers employ gaskets that only fit specific containers. For example, Mason jar lids employ narrow, circular, flexible elastomeric gaskets that are bonded to the lids' outer perimeter. Consequently, a lid that fits a Wide Mouth Mason jar will not fit a Regular-Size Mason jar, and vice versa. Although the narrow width of the flexible elastomeric gasket of Wide Mouth lids could be increased to cover the mouth of Regular-size Mason jars, doing so would significantly increase the lids' cost. Finally, Mason jar lids are secured to Mason jars by means of threaded metal collars whose threads match those of the Mason jar. Hence a Wide Mouth Mason Jar lid of any type cannot be secured to Regular size Mason jar by customary means. Accordingly, until now, flexible elastomeric gaskets have been designed to only fit the mouths of specific food storage containers, and not the mouths of a wide range of food containers.
Consumers like rectangularly-shaped food containers because they (1) accommodate rectangularly-shaped food items (such as sandwiches), and (2) efficiently fit inside rectangularly-shaped refrigerators. However, re-enterable circular-shaped food containers can remain air-tight more reliably than re-enterable rectangularly-shaped food containers. This is because the free edges (i.e. the edges around openings) of food storage containers deform under a vacuum, thereby creating unequal sealing pressure along the free edges of asymmetric containers. Leaks occur at low pressure points along a food container's flexible elastomeric gasket. This unfavorable characteristic of rectangularly-shaped seals (i.e. “seal” defined as the interface between two mating parts) is why the old Bell System (AT&T) only employed circular gaskets on its water-proof metal cases that enclosed spliced communications cables. Such splice cases remained air-tight and waterproof in the uncontrolled outdoor environment for 40 or more years over temperatures ranging from 115 degrees to minus 40 degrees Fahrenheit. Accordingly, it is desirable for a versatile vacuum lid structure (i.e., a vacuum lid structure capable of fitting a variety of different size food container openings) to have a circular shape and employ circular gaskets. A circular vacuum lid can even work on rectangular-shaped food storage containers provided the flexible elastomeric gasket affixed to the vacuum lid is sufficiently thick and compliant to compensate for vacuum-induced geometric distortions of the circular vacuum lid. Of course, the previously-mention indirect approach is always available wherein a rectangularly-shaped container is vacuum packed by placing it in a larger circular container.
The wide range of food container openings that exist makes it challenging to devise a space-efficient, cost-effective monolithic vacuum lid structure capable of mating with all food containers and have sufficient strength to resist vacuum-induced forces. A brute-force approach might be to employ a flat-bottom structure whose outside diameter was large enough to cover the opening of any food container of interest. However, the cost of covering the entire bottom of such a structure with a suitable elastomeric sealing material would make the structure prohibitively expensive. Further, such a large structure would be space-inefficient in that it would take up a disproportionate amount of space inside refrigerators when used on small or medium-size containers. Analytically, space efficiency is defined herein as the largest diameter of the vacuum structure minus the largest diameter of the food storage container, divided by the largest diameter of the food storage container. There is also the issue of strength. The atmospheric pressure of approximately 14.6 pounds per square exerts approximately 100 pounds on both sides of a 3-inch diameter Mason jar lid. The corresponding pressure on a lid covering a 10-inch pie pan would be approximately 1,100 pounds. Thus, the asymmetric forces on the lid of even a partially vacuumed container can be quite large. The uniformly distributed atmospheric loads exerted on the top of conventionally-designed vacuum lids can cause them to severely sag downward into the food container, and even fracture. Accordingly, a versatile vacuum lid structure must not only be adaptable to efficiently fit a variety of container openings, but also strong enough to effectively resist large vacuum-induced forces and deformations (sagging). An approach for minimizing sagging at the center of a vacuum lid structure is to employ methods that shift the area where atmospheric loads are resisted away from the center and outward toward the periphery of the vacuum lid structure, as described herein.